1. Field of the Invention
The present invention relates generally to an image forming apparatus, an image forming method, and a computer-readable storage medium.
2. Description of the Related Art
Electrophotographic image forming apparatuses typically use wall-outlet power supply (commercial power supply) as external power source. The commercial power supply is electrical power supplied from a power plant of an electric-power company to indoor electrical appliances and the like through transmission lines. If a transmission line, power distribution equipment, or the like of the commercial power supply is struck by lightning or animal or bird contact, the voltage of the commercial power supply can drop instantaneously (which may be referred to as “instantaneous voltage drop”). This instantaneous voltage drop can cause a trouble such as malfunction or outage of an indoor electrical appliance, which may be an electrophotographic image forming apparatus. Some type of electrical appliances such as electrophotographic image forming apparatuses is configured to tolerate instantaneous voltage drop in the commercial power supply for a short period of time, e.g., 10 ms (milliseconds), by employing a capacitor such as an electrolytic capacitor with large capacitance in a converter of a built-in switched-mode power supply device such as a PSU (power supply unit). Some type of electrical appliances such as electrophotographic image forming apparatuses is configured to tolerate even a long-duration power failure of 20 milliseconds or longer, for example, by including or externally connected to an uninterruptible power supply device.
Conventionally, such an electrophotographic image forming apparatus is generally configured to receive power supply from a switched-mode power supply device built in the image forming apparatus until the built-in switched-mode power supply device reaches its power-supply capability limit. However, there is a variation in the power-supply capability of the built-in switched-mode power supply device at occurrence of instantaneous voltage drop. This variation can prevent smooth, malfunction-free switching of power supply source from the built-in switched-mode power supply device to a power storage unit. Furthermore, such a conventional electrophotographic image forming apparatus requires that the power supply source should be switched from the built-in switched-mode power supply device to the power storage unit immediately upon occurrence of instantaneous voltage drop so that the power supply source can be switched smoothly. However, this leads to wasting consumption of the expensive power storage unit having a limited usable life.
Therefore, there is a need for an image forming apparatus, an image forming method, and a computer-readable storage medium, capable of prolonging the usable life of the expensive power storage unit by using a power storage unit having a limited usable life less frequently.